1. Field of the Invention
The present invention relates to an apparatus and method for encoding a wobble signal to be recorded as physical address information on an optical disc such as a writable compact disc (CD) or digital versatile disc (DVD), and an apparatus and method for decoding a wobble signal read from the optical disc.
2. Description of the Related Art
It is common that a writable optical disc, such as a digital versatile disc-random access memory (DVD-RAM) or digital versatile disc-re-writable (DVD-RW), has grooves formed along spiral or concentric tracks. Here, portions of the optical disc other than the grooves are typically called lands. Data can be recorded on only any one or both of each groove and each land according to a writing method. A specific variation is applied to a wall of each groove in a groove formation process, and a specific frequency signal is generated based on the specific variation in a recording/reproduction process, so it can be used as auxiliary clock means. Here, the specific variation is called a wobble and the specific frequency signal is called a wobble signal.
On the other hand, physical address information must be pre-recorded on the optical disc. A description will hereinafter be given of wobble addressing methods for forming and recording physical address information on the optical disc in the form of a wobble.
A wobble addressing method based on complementary allocated pit addressing (CAPA) is used for a DVD-RAM, and a wobble addressing method based on land pre-pit addressing is used for a DVD-RW. In addition, a wobble addressing method based on minimum shift keying (MSK) modulation has been proposed.
In the MSK modulation-based wobble addressing method, as shown in FIG. 1, two different frequencies f1 and f2 and two different phases P1 and P2 are decided based on a combination of an inphase message mI and quadrature message mQ of wobble data to be formed and recorded as physical address information on the optical disc, and wobble signals with four different waveforms are generated according to the two different frequencies and the two different phases.
For example, the first one f1 of the two different frequencies f1 and f2 is higher than a center frequency fc and the second frequency f2 is lower than the center frequency fc. Also, the first one P1 of the two different phases P1 and P2 is zero and the second phase P2 is 180° (π). As a result, an MSK-modulated wobble signal having four different waveforms generated according to the first and second frequencies and the first and second phases, namely, cos(2πf2t+0), cos(2πf1t+0), cos(2πf1t+π) and cos(2πf2t+π) can be expressed by the following equation:
                                                                                          S                  MSK                                ⁡                                  (                  t                  )                                            =                            ⁢                                                                                          m                      I                                        ⁡                                          (                      t                      )                                                        ⁢                                                            ϕ                      1                                        ⁡                                          (                      t                      )                                                                      +                                                                            m                      Q                                        ⁡                                          (                      t                      )                                                        ⁢                                                            ϕ                      2                                        ⁡                                          (                      t                      )                                                                                                                                              =                            ⁢                                                                                          m                      I                                        ⁡                                          (                      t                      )                                                        ⁢                                      cos                    ⁡                                          (                                                                        π                          ⁢                                                                                                          ⁢                          t                                                                          2                          ⁢                                                                                                          ⁢                                                      T                            b                                                                                              )                                                        ⁢                                      cos                    ⁡                                          (                                              2                        ⁢                        π                        ⁢                                                                                                  ⁢                                                  f                          c                                                ⁢                        t                                            )                                                                      +                                                                                                      ⁢                                                                    m                    Q                                    ⁡                                      (                    t                    )                                                  ⁢                                  sin                  ⁡                                      (                                          π                                              2                        ⁢                                                                                                  ⁢                        T                                                              )                                                  ⁢                                  sin                  ⁡                                      (                                          2                      ⁢                      π                      ⁢                                                                                          ⁢                                              f                        c                                            ⁢                      t                                        )                                                                                                          [                  Equation          ⁢                                          ⁢          1                ]            where, Tb represents a wobble data bit duration.
On the other hand, a combination of the inphase message mI and quadrature message mQ of wobble data to be recorded on the optical disc must always be expressed as (mI, mQ). In this regard, in the case where wobble data to be recorded on the optical disc has a bit stream ‘11010000’ as shown in FIG. 2, a combination (mI, mQ) of the inphase message mI and quadrature message mQ of the first bit ‘1’ becomes (1,1) by a combination with the second bit ‘1’, a message combination (mI, mQ) of the second bit ‘1’ becomes (0,1) by a combination with the third bit ‘0’, a message combination (mI, mQ) of the third bit ‘0’ becomes (1,0) by a combination with the fourth bit ‘1’, a message combination (mI, mQ) of the fourth bit ‘1’ becomes (0,1) by a combination with the fifth bit ‘0’, and a message combination (mI, mQ) of the fifth bit ‘0’ becomes (0,0) by a combination with the sixth bit ‘0’. That is, a combination (mI, mQ) of the inphase message mI and quadrature message mQ of a wobble data bit is any one of (1,1), (1,0), (0,1) and (0,0), and signals corresponding thereto have four different waveforms with two different frequencies and two different phases, as shown in FIG. 2.
Therefore, an MSK-modulated wobble signal SMSK (t) has a smoothly consecutive waveform resulting from the summing-up of the above signals, so it can be more accurately recorded on the optical disc.
On the other hand, a conventional decoding apparatus for decoding an MSK-modulated wobble signal read from the optical disc comprises, as shown in FIG. 3, analog mixers 10 and 11, interval integrators 12 and 13, phase decision devices 14 and 15, and a logic circuit 16.
The analog mixers 10 and 11 multiply a wobble signal read from the optical disc by first and second encoding frequencies φ1(t) and φ2(t) to extract wobble signals of specific frequencies, respectively. The interval integrators 12 and 13 integrate the extracted wobble signals of the specific frequencies for predetermined intervals, respectively. The phase decision devices 14 and 15 compare the integrated values with a predetermined threshold value (Threshold=0) to decide phases, respectively. The logic circuit 16 interleaves the decided phases to restore a binary sequence of bit stream data (i.e., original wobble data). As a result, an MSK-modulated wobble signal, recorded in a smoothly consecutive waveform according to the MSK modulation method, is demodulated into wobble data with no high-frequency noise by the decoding apparatus with the above-mentioned construction.
However, the above-mentioned conventional decoding apparatus has a disadvantage in that a complex hardware configuration is required to multiply a wobble signal read from the optical disc by the first and second encoding frequencies φ1(t) and φ2(t) and integrate the resulting signals.
Further, in the case where the optical disc varies in rotational speed by a spindle servo operation of an optical disc apparatus, the wobble signal read from the optical disc varies in frequency, so the first and second encoding frequencies φ1(t) and φ2(t) applied respectively to the analog mixers 10 and 11 must vary. To this end, a complex hardware configuration and demodulation algorithm must be provided in the decoding apparatus.